If people lived 800 years, then they would probably be able to figure out things like reverse osmosis.
Really? Could you please discuss the scientific background knowledge required and the technology needed to construct such a device, and why you think that increased lifespan
only in the Bronze Age would have been all that was needed for someone to figure it out?
Then please discuss why, in light of the fact that fresh water is a universal and critical need, it was forgotten?